In recent years, the popularization of cellular phones has increased demand for voice communication or data communication through cellular phones from indoors as well as outdoors. With such an increase in demand, the development of microminiature base stations capable of being installed indoors such as users' premises or small offices has progressed. The coverage of such a base station is extremely small compared to the coverage of a base station installed outdoors (hereinafter, referred to as a macro base station), and thus is referred to as a femtocell. Hereinafter, the microminiature base station is referred to as a femtocell base station. As an operation form of the femtocell base station, it has been investigated that only a mobile station which has been previously registered is connected to the femtocell base station and performs communication therewith.
FIG. 5 is a configuration diagram of a wireless communication system 1000 including a femtocell base station 101. The reference numeral 101 denotes a femtocell base station, and forms a femtocell 106. The femtocell base station 101 is connected to a network 105 through a femto gateway (GW) 104. The reference numerals 102 and 103 denote a mobile station. When the mobile stations exist in the femtocell 106, the registered mobile station 102 registered with the femtocell base station 101 can be connected to the network 105 through the femtocell base station 101. The unregistered mobile station 103 which is not registered with the femtocell base station 101 cannot be connected to the network 105 through the femtocell base station 101.
The above-mentioned wireless communication system 1000 transmits a pilot signal toward the femtocell 106 within the range covered. The registered mobile station 102 performs synchronization establishment, channel estimation and the like by receiving the pilot signal, and transmits and receives data to and from the femtocell base station 101. For this reason, the pilot signal can be received in the registered mobile station 102 with good quality, thereby allowing good communication quality to be provided.
In addition, as a technique capable of being applied to the above-mentioned wireless communication system 1000, the following technique is proposed.
In a wireless communication system disclosed in Patent Document 1 (Japanese Unexamined Patent Publication No. 2008-17325), when a wireless device interfering with the communication with a wireless base station is detected, a wireless terminal device (mobile station) belonging to the wireless base station transmits a control signal to the wireless device. Thereby, it is possible to control the wireless base station even when it is a wireless device of an interference source which is not capable of being identified, and to avoid a radio wave interference.
Base stations included in a wireless communication system (mobile communication system) disclosed in Patent Document 2 (Japanese Unexamined Patent Publication No. 2006-135673) control transmission power of a pilot channel based on the total transmission power or the upstream interference amount in a peripheral base station. Thereby, the transmission power of the pilot channel is autonomously set while performing an emphasis between the base stations, and thus the cell formation is possible.
In Non-patent Document 1, a system is proposed in which when a specific signal for an operation is received from the mobile station, a femtocell base station operates. It is examined that the femtocell base station is used in systems such as wideband code division multiple access (W-CDMA), evolved universal terrestrial radio access (E-UTRA), and long term evolution (LTE) in the wireless communication standard of the cellular phone, and is used in systems such as IEEE 802.16m in the wireless communication standard of wireless metropolitan area network (wireless MAN).
When the femtocell base station is used in W-CDMA, as disclosed in Non-patent Document 2, data transmission using an individual channel in the uplink and the downlink of which transmission power is controlled or data transmission using a shared channel in the downlink is performed.
When the femtocell base station is used in E-UTRA, as disclosed in Non-patent Document 3, data transmission is performed in which the band of the wireless frequency is divided into a plurality of resource blocks (PRB; Physical Resource Block), a scheduler included in a base station performs allocation of the PRBs, and the allocated PRBs are used.
When the femtocell base station is used in IEEE 802.16m, as disclosed in Non-patent Document 4, data transmission is performed in which orthogonal frequency division multiple access (OFDMA) is adopted as a communication standard to divide the band of the wireless frequency into subcarriers, a scheduler included in a base station performs allocation of the subcarriers, and the allocated subcarriers are used.